Project Summary/Abstract The goal of this project is to investigate the potential of transcranial stimulation to enhance intelligibility in speech mixtures in older adults struggling in these environments. Many older adults with and without sensorineural hearing loss (SNHL) struggle with speech-on-speech (SOS) understanding, likely as a result of a mixture of peripheral and central deficits in the auditory system. Whereas the peripheral deficits represent a hard limit on performance, central deficits may be improved with experience and training. There are many auditory training programs available that aim to optimize a listener’s performance in SOS environments, but the benefits of these programs can be small and variable across listeners. Recent evidence shows that transcranial alternating current stimulation (tACS) – a safe and non-invasive low level of current applied to the scalp – can lead to improved speech-in-noise understanding in young normal hearing (NH) listeners and older adults with SNHL during the course of stimulation. Furthermore, transcranial stimulation studies in other domains show that it can enhance benefits from cognitive training in older adults, with effects persisting for months. However, it is not known if tACS can enhance intelligibility or reduce listening effort for SOS in older adult listeners specifically struggling with SOS understanding, or if tACS can enhance benefits from auditory training during or beyond the course of stimulation. In this exploratory R21 proposal, older adults reporting and demonstrating struggles in speech mixtures will be randomly assigned to Active tACS or Sham tACS groups. All participants will be tested in the first visit on a baseline SOS recognition task, and again on a SOS task with Active or Sham tACS. Participants will then complete two weeks of computer-based auditory training at home (the Listening and Communication Enhancement, “LACE”, program; Sweetow and Sabes, 2006). Participants will visit the lab twice during the LACE training period to undergo Active tACS or Sham tACS during the SOS task. Listening effort will be assessed via pupillometry measured concurrently with the SOS task and via a questionnaire through the LACE program. Performance on the SOS task will be re-assessed at 4 weeks following enrollment in the study to assess retention of benefits. By comparing the in-laboratory change in SOS performance and listening effort in the Active and Sham groups relative to baseline in the first visit, this project aims to determine if tACS can improve speech intelligibility and/or reduce listening effort in listeners who struggle with SOS (Aim 1). By comparing LACE performance and SOS performance and listening effort at all subsequent visits, this project aims to determine if tACS can increase benefits obtained from an auditory training program over the short and long term (Aim 2). Ultimately this work could significantly improve the communication abilities of listeners with and ...